Recently, the uses for hot melt adhesives have been undergoing rapid expansion as pressures to eliminate solvent based adhesives for health, safety and environmental reasons increase throughout industry. This, in turn, has led to investigations of systems offering new properties which allow hot melts to be more widely used. Pressure sensitive hot melts, such as described in U.S. Pat. No. 4,622,357, and hot melts displaying extended open times of several minutes to as long as several hours, such as described in copending applications Ser. Nos. 07/385,515, filed Jul. 25, 1989 and 07/213,789, filed Jun. 30, 1988, assigned to the same Assignee hereof and incorporated herein by reference, are examples of the novel systems currently being developed.
A significant limitation of hot melt adhesives, however, is their limited heat resistance. Formulations which are readily flowable at 177.degree.-204.degree. C. (350.degree.-400.degree. F.), the typical operating temperatures of conventional application machinery, will soften and lose bonding strength at much lower temperatures. Hot melt adhesives are known which give relatively good heat resistance such as polyamides, polyesters, and reactive systems but they have other undesirable properties. Polyamide based hot melts, for instance, that give good thermal resistance usually have very poor ambient and low temperature flexibility and short open times.
There, therefore, exists a need for new hot melt formulations which display better high temperature resistance without sacrificing low temperature properties and open times. Such adhesive formulations should be non-reactive and be widely variable in composition so that those skilled in the art can exhibit the high temperature resistance in compositions displaying other desired properties, such as permanent pressure sensitive properties, extended open time, flexibility, better solvent, or plasticizer resistance, etc.